Phage selection for bacterial cheats leads to population decline

Area of Science:

• Microbial ecology
• Evolutionary biology
• Bacteriology

Background:

• Predators and parasites influence bacterial populations, but their role in bacterial social evolution is understudied.
• Siderophores are crucial for iron acquisition in bacteria, but their production is vulnerable to exploitation by non-producing 'cheater' genotypes.

Purpose of the Study:

• To investigate the impact of lytic phages on the competition between siderophore-producing and non-producing bacterial genotypes.
• To understand how phage presence affects bacterial social evolution and public goods dynamics.

Main Methods:

• A selection experiment using 140 populations of Pseudomonas aeruginosa PAO1 over ~20 bacterial generations.
• Assessing the competition between siderophore producers and non-producers under varying conditions, including the presence of lytic phages.

Main Results:

• Lytic phages consistently favored non-producing genotypes in competition, irrespective of siderophore reliance for iron uptake.
• Phage pressure led to increased siderophore production, imposing a cost on producers and facilitating outcompetition by non-producers.
• Despite initial advantages for cheaters, high cheating loads reduced mixed population fitness, with producer monocultures being the only survivors under essential siderophore conditions.

Conclusions:

• Natural enemies like phages can modulate public goods production, impacting bacterial social strategies.
• The interplay between predation, cheating, and public goods is critical for understanding bacterial social evolution and population dynamics.